Plasma plumes protect Earth from space weather

NASA researchers report the discovery that material in the Earth’s plasmasphere can aid in preventing particles from the Sun from entering into the near-Earth environment. The finding helps researchers determine the best way to protect orbiting spacecraft from the effects of space weather, including coronal mass ejections (CMEs) and the constant stream of particles from the solar wind.

For the first time, a NASA study shows that in certain circumstances, a band of dense particles normally circling Earth that are found deep inside the magnetosphere can extend a long arm out to meet – and help block – incoming solar material.

The scientists published their findings in the March 6 issue of the journal Science Express, in which they compared observations from the ground and in space during a solar storm on January 17, 2013.

This was a moderate solar storm caused by a CME striking Earth’s magnetosphere for several hours. When the CME encountered the boundary of the magnetosphere, its magnetic fields and those around Earth realigned in a process called magnetic reconnection, which allowed energy and solar material to traverse the boundary into the magnetosphere. NASA’s three THEMIS – for Time History of Events and Macroscale Interactions during Substorms – spacecraft were ideally placed during the event, flying through the magnetosphere’s boundary approximately 45 minutes apart, and caught this interaction.

Nearer to Earth, scientists could also study the sphere of cold, dense gas at the top of the atmosphere. This region is dubbed the plasmasphere and, as its name implies, it is a gaseous sphere made of charged particles. GPS signals travel through the plasmasphere and travel at different speeds, depending on how thick or thin the plasmasphere is along the journey. Consequently, tracking the GPS radio signals can help researchers map out the characteristics of the plasmasphere.

THEMIS showed that the reach of this cold, dense plasmasphere material stretched to the magnetic reconnection point where the CME made contact with the magnetopause. The three sets of THEMIS observations confirmed that the plume had a remarkable impact on the characteristics of the magnetic reconnection region.

“It wouldn’t work if the magnetic reconnection happened for only a few minutes,” explained David Sibeck the project scientist for THEMIS at NASA Goddard. “But if it lasts long enough, the whole magnetosphere gets involved. This tongue of the plasmasphere surges out, adding another layer of protection, curbing the magnetic reconnection.”